In the prior art, complex-mixing methods are used to obtain the fertilizers with all three elements of nitrogen, phosphorus and potassium, for example, combination of carbamide with potassium dihydrogen phosphate, or mixture of carbamide, calcium phosphate and potassium sulfate. In order to reduce the pollution of fertilizer runoff to the environment, especially to water bodies, slow (controlled)-release fertilizer has become the focus of researches and applications. But the currently available slow-release and controlled-release fertilizers generally adopt coating methods, for example, coating carbamide with a layer of urea-formaldehyde resin film, the coating film is damaged gradually as urea-formaldehyde resin degrading so as to slowly release the fertilizer. WO2003/082005 discloses a preparing method for highly dispersed urea-formaldehyde polymer fertilizer slow-release agent. This polymer achieves slow release of nitrogen fertilizer and the mixture of calcium carbonate, plaster, metallic silicate, talcum powder, sulfur, active carbon, chelated iron, zinc and manganese is added into granulating process. But the material cannot supply phosphorus and potassium needed for crop growth after the material degrades. U.S. Pat. No. 19,810,288,456 discloses a preparing method for solid urea-formaldehyde polymer slow-release fertilizer comprising preparing a liquid mixture of carbamide, formaldehyde and ammonia, heating and acidifing the mixture to start the polymerization of methylene urea, and heating to finish the polymerization of methylene urea, then drying the obtained product which cannot provide phosphorus and potassium needed for crop growth after it degrades in soil. In JP10259083, fertilizer is added into pipes which are biologically degradable polymer, then holes are drilled on the pipes with a certain intervals so that the fertilizer can be released slowly in soil. When the product of JP10259083 is used, the nutrients that the soil can get depend upon the fertilizer ingredients filled into the pipes.